The present application is a 371 National Stage of co-pending application PCT/DE00/03213 having an international filing date of Sep. 15, 2000, and a priority date of Sep. 17, 1999, entitled xe2x80x9cDevice for Laminating A Layered Structure Consisting of At Least Two Plastic Strips in Sectionsxe2x80x9d.
1. Field of the Invention
The invention relates to a device according to the precharacterizing clause of claim 1 for laminating in sections a layered structure consisting of at least two plastic strips, comprising successively formed panels with designs, for producing plastic cards along a conveying path, comprising successively arranged heating and cooling devices, which are formed by individual temperature-controllable pressing elements which accommodate an integer number of panels and are arranged on a common support, and a drive unit, which displaces mutually facing pressing bands which can be driven intermittently in a conveying direction and between which the plastic strips can be moved in sections through the heating and cooling devices.
2. Related Art
EP-B-0 134 820 describes a device which, for a continuous production of plastic cards, in particular credit cards, check cards, access cards etc., allows a synchronous feed of plastic strips into a laminating installation for the forming of a laminate. The plastic strips consist of individual panels which are separate from one another and are arranged one behind the other in one or more rows. The laminating installation comprises heating and cooling devices made up of temperature-controllable pressing elements which are arranged on a longitudinal support and the dimensions of which are chosen for the treatment of an integer number of panels at a time and allow baking in sections of the plastic strips forming a layered structure, with subsequent cooling. By arrangement between mutually facing endless pressing bands which can be driven in a cyclical manner, the at least two plastic strips are moved into treatment zones for the pressing elements, in which the heating-pressure effect and the cooling-pressure effect is transferred to the plastic strips. The plastic strips are laminated in sections as a result. For this purpose, the pressing elements respectively comprise a fixed lower pressing bar and a movable upper pressing bar, between which the pressing bands come into contact during the heating/cooling-pressure treatment.
However, it has been found to be disadvantageous that, in rapid treatment, the temperature-controlled web with high temperatures of the plastic strips to be laminated lead to high local instances of expansion and shrinkage of the pressing bands and possibly of the plastic strips, to be precise in particular in the edge region of the pressing zones, where discontinuous temperature and pressure conditions prevail. This leads to high loading with compressive and tensile forces and possibly to damage of the pressing bands, so that they are subject to a high degree of wear. If, to increase the rate of production, the shortest dwell times are used for heat treatment, but, to compensate for this, high temperatures, this disadvantageous wear increases. Furthermore, laminating defects occur at the panels and lead to an undesired rejection rate, since there is a high requirement for the surface of such plastic cards to be defect-free.
DE-C-42 05 746 describes a device for adhesively bonding sheet-like workpieces, in particular for concealing plastic parts in sheet form, in which a depositing station, a heating station, a pressing station and a cooling station, arranged outside the pressing station, are successively arranged. The workpieces to be adhesively bonded are passed individually in succession by means of a lower transporting belt first through the heating station and subsequently through a pair of pressing rolls of the pressing station. The pressing station, defined by the pair of pressing rolls, serves at the same time as a deflecting roller for transporting belts and is not movable with respect to the conveying path. The heating station comprises two heating plate units, which respectively has a link chain comprising a plurality of chain links, on which there are mounted transverse supports, which run transversely with respect to the conveying direction and have heating elements. The links of the link chain are respectively connected via intermediate links on both sides to a drive cylinder, via a driving shaft, by the actuation of which cylinder the two link chains of the heating plate units can be configured such that they are parallel to each other, bulging out substantially in the same direction or else converging in a wedge-shaped manner. Although the link chains of the heating plate unit are adjustable, this adjustment does not permit a movable arrangement of the heating elements, or even of the pressing station, nor the movement in the direction of the conveying path, on account of the static adequately determined fixed position of the drive cylinders. A cooling press is not provided. The position of the chain links is static.
It is the object of the invention to provide a device which allows the production of plastic cards with high laminating quality at high rates of production.
This object is achieved according to the invention by burning a device for laminating the layered structure consisting of at least two plastic strips in sections including successively formed panels with designs for producing plastic cards along a conveying path. The device includes successively arranged heating devices and cooling devices, which are formed by individual temperature-controllable pressing elements, wherein each pressing element accommodates an integer number of panels, and wherein the pressing elements are arranged on a common support. A drive unit is provided which displaces mutually facing pressing bands, wherein the pressing bands can be driven intermittently in a conveying direction, and wherein plastic strips can be moved in sections between the pressing bands through the heating and cooling devices. The pressing elements are arranged such that they can be moved in the direction of the conveying path against a restoring force, which acts toward their initial position.
This provides a device for laminating in sections a layered structure consisting of at least two plastic strips, comprising successively formed panels with designs, for producing plastic cards along a conveying path, which device transfers the temperature-induced local changes in length of the pressing bands to the positioning of the pressing elements, by the latter being able to follow axial displacements and thereby permit a compensation to take place. Undesired loads of the pressing bands and of the plastic strips in the longitudinal direction are avoided as a result. Consequently, operation even with short cycle times and resultant high temperatures is possible without any defects occurring.
It is advantageous in this case that, by incorporating in the design a dissipation of the axial distortion forces occurring, the device responds directly, so that it is possible to dispense with complex controllers for this purpose.
The device according to the invention advantageously decouples adjacent pressing elements, so that the pressing elements can have a slight change in their distance from each other in the conveying direction. This makes it possible for the cyclically or intermittently driven pressing bands and the plastic strips lying in contact with them, which are exposed to locally different temperatures on account of the differently temperature-controlled pressing elements, to be positioned precisely in the pressing elements. The stresses otherwise acting on the pressing bands or plastic strips are greatly reduced as a result.
In an advantageous configuration of the invention it is provided that, during a stop in production, a raising device, raising the upper pressing bar, can be actuated for further opening of the pressing elements, the opening movement of the upper pressing bar being small in normal operation, to permit the advancement of the pressing bands. Also provided is a lifting device, which, in the event of a stop in production, raises the pressing bands simultaneously, in order to interrupt a contact bridge between the pressing bands and the lower pressing bar during the opening of the pressing element. As this happens, the pressing bands are displaced into an approximately centrally arranged position between the lower and upper pressing bars. Undesired overheating of the pressing bands is avoided as a result, since the pressing bands then only serve as heat-transferring means during the heating-pressure treatment itself. This significantly increases the service lives of the pressing bands. In particular in the case of a fault or maintenance, overheating of the plastic strips, which would otherwise result in extensive setting-up work, is effectively prevented.
The pressing bands are expediently placed in each case over a running-in drum, arranged outside the pressing elements, and a running-out drum. At least one of the drums has a peripheral portion with precision spikes, which is in drive connection with a transporting perforation provided in an edge zone of an assigned pressing band. The spiked portion permits exact registration and slip-free guidance of the pressing band. The height of the spikes is about 0.5 mm.
The spikes have an upwardly rounded form. Each of the drums is preferably provided with a spiked portion, the running-in drums and the running-out drums being offset in relation to one another to avoid the spikes hitting one another. The offset of the drums in the running-in region and in the running-out region is preferably identical and in the same direction, so that an identical band can be used for both pressing bands.